Burner apparatus for producing glass fibers



Dec. 15, 1970 o. E. su-nsuzn BURNER APPARATUS FOR PRODUCING GLASSFIBERS2 Sheets-Sheet 2 Filed April 12, 1968 INVEN m Donmfl E.SHI$L$ UnitedStates Patent O 3,547,568 BURNER APPARATUS FOR PRODUCING GLASS FIBERSDonald E. Shisler, Napoleon, Ohio, assignor to Johns- ManvilleCorporation, New York, N.Y., a corporation of New York Filed Apr. 12,1968, Ser. No. 720,915 Int. Cl. F23r N US. Cl. 431-158 13 ClaimsABSTRACT OF THE DISCLOSURE I An improved burner apparatus and method foruse in the flame attenuation of glass filaments; The burner includes arefractory combustion tunnel having laterally elongated inlet and outletopenings for generating a relatively wide and flat hot gaseous blast ofhigh temperature and high velocity for attenuating glass filaments. Athermally conductive orifice plate having a laterally elongated andvertically restricted orifice is positioned adjacent the inlet end ofthe tunnel and functions to pass a combustible gas mixture into thetunnel. The orifice has a width similar to that of the tunnel, but theheight of the orifice is substantially smaller than the height of thetunnel. A plenum unit is located between the conduit through which thecombustible gas mixture is supplied and the orifice and acts on thecombustible gas mixture as it moves toward the orifice so that thecombustible gas mixture as it moves through the orifice is distributeduniformly throughout the lateral and vertical extent of the orifice andissubstantially free of all eddies and turbulence. This constructionprovides relatively high gas velocity over a wide range of flow rateswith relatively low back pressure upstream of the tunnel inlet andwithout any flashback problem.

DESCRIPTION OF THE INVENTION This invention relates generally to theprocessing of glass filaments and, more particularly, to an improvedburner apparatus and method for generating a wide and flat hot gaseousblast for attenuating glass filaments.

It is common practice in the fiber glass industry to produce amultiplicity of continuous primary glass filaments simultaneously from asingle melting pot, and then subject the filaments to a continuous hotgaseous blast to re duce the primary filaments to fine fibers for use asinsulation or the like. As technological advances have permitted thenumber of filaments produced from a single melting pot to be increased,it has become increasingly difficult to provide a wider burner whichproduces a gaseous blast sufiicient to attenuate all the filamentsuniformly, especially over long operating periods, while also achievinga long burner life. More particularly, one of the specific problemsencountered has been how to increase the gas quantity flow rate throughthe burner at the required velocity without excessive increases in theback pressure and/or flashback problems. (As is well known to thosefamiliar with this art, a flashback occurs when the flame from theburner tunnel flashes back through the tunnel inlet into the upstreamequipment.)

It is, therefore, a primary object of the present invention to providean improved tunnel-type burner apparatus and method for flameattenuating glass filaments which provides relatively high gasvelocities and flow rates through the tunnel with relatively low backpressure upstream of the tunnel inlet, and yet has little or no tendencyto produce flashbacks at low quantity throughput. In this connection, arelated object of the invention is to provide such an improved burnerapparatus and method which produces a wider attenuation blast than mostburners proposed heretofore while maintaining the flow of incoming gasesat the orifice with a velocity greater than the flame propagation speed.

Another object of this invention is to provide an improved burnerapparatus and method of the foregoing type which provides a relativelylarge heat transfer surface in the area adjacent the inlet end of thetunnel so as to maintain a relatively low temperature upstream of thetunnel inlet. A related object of the invention is to provide such animproved burner apparatus and method which provides a relatively largeheat transfer surface directly at the orifice leading into the inlet endof the tunnel.

It is a further object of the present invention to provide an improvedburner apparatus and method of the type described above which achievesrelatively high gas velocities and flow rates into and through thetunnel while maintaining a relatively small orifice area at the inletand which provides a practically unlimited turn down range. Moreparticularly, it is an object to provide such an improved burnerapparatus and method which permits the combustion gas flow rate to berelatively low without flashback, and which extinguishes any flame thatpenetrates through the inlet orifice when the flow rate approaches theOE level.

A still further object of the invention is to provide such an improvedburner apparatus and method which achieves all the above objectives incombination with good flame characteristics in the burner output.

Still another object of the invention is to provide such an improvedburner apparatus which can be efliciently manufactured at a low costfrom readily available materials.

Yet another object of the invention is to provide such an improvedburner apparatus which is stable and reliable over relatively longoperating periods.

Other objects and advantages of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a cross sectional elevation view of a burner apparatusembodying the present invention;

FIG. 2 is a horizontal section taken along line 22 in FIG. 1;

FIG. 3 is an end elevational view of that portion of the burner attachedto the inlet end of the combusion tunnel, with a fragment thereof brokenaway to show the inlet orifice to the combustion tunnel; and

FIG. 4 is a vertical section taken along line 4-4 in FIG. 3.

While the present invention is susceptible of various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the draw ings and will herein be described in detail. Itshould be understood, however, that it is not intended to limit theinvention to the particular forms disclosed, but, on the contrary, theintention is to cover all modifications, equivalents and alternativesfalling within the spirit and scope of the invention as expressed in theappended claims.

Turning now to the drawings and referring first to FIG. 1, there isshown a burner 10 forming a refractory tunnel 11 for producing a hotgaseous blast suitable for use in flame attenuating a multiplicity ofprimary glass filaments, so as to reduce the filaments into fine fibers.The tunnel 11, which is formed by a plurality of refractory componentsencased by a metal housing 12, is laterally elongated along its entirelength as can be seen in FIG. 2, for example. A major portion of thetunnel extending rearwardly from the outlet opening 11a is of uniformcross section, but the inlet opening 11b has a vertical dimensiongreater than that of the outlet opening 11a, with the bottom wall 110 ofthe tunnel tapering upwardly from the lower edge of the inlet openingtoward the outlet opening. This feature, combined with the offsetposition of the inlet orifice to be described below, has been found toprovide increased flame stability and reduced erosion of the refractorywalls.

A number of different refractory materials may be used to form thetunnel 11 within the metal housing 12. In general, it is preferred touse a high density material to form the walls of the tunnel, so as towithstand the eroding effects of the high temperature and high velocitygases within the tunnel, while the materials spaced away from the tunneltoward the metal housing 12 are selected to have lower density andgreater thermal insulating properties. Since the most severe erosionoccurs in the forward portion of the tunnel, because of the highertemperature and the expanding volume of the gases in the forward region,the tunnel walls near the inlet end thereof may be made of a materialthat is somewhat less dense, and better insulating, than the material inthe forward portion of the tunnel. A number of different refractorymaterials which satisfy the above criteria are known to those to thoseskilled in this art, but in one exemplary embodiment of the inventionthe forward tunnel wall components 13 are made of a castable refractoryhaving a density on the order of about 100 lbs./ft. such as the aluminumoxidecalcium aluminate composition marketed by the Norton Company anddesignated 33-1; the rear tunnel wall components 14 are made of a lowerdensity material such as the highly pure kaolin clay marketed by theBabcock and Wilcox Company and designated K-30 with a density of 52.3lbs./ft. the outer components 15 are made of a more highly insulatingmaterial such as the castable refactory marketed by Johns-ManvilleCorporation and designated CA-Insulating Firecrete; and the component 16beneath the rear tunnel wall component is made of a sillca felt marketedby Johns-Manville Corporation and designated Micro-Quartz felt.

In accordance with the present invention, a thermally conductive orificeplate is mounted on the inlet end of the refractory tunnel, and a plenumunit is connected between the orifice plate and a supply conduitconnected to a source of a combustible gas mixture, with the orificeplate and plenum cooperating to form a passageway terminating in asingle laterally elongated orifice substantially as wide as the inletopening of the combustion tunnel and more restricted than the inletopening in the vertical dimension. Also, the walls of the plenum unittaper gradually from the supply conduit to the orifice to providelaminar flow, that is substantially free of all eddies and turbulence,of the combustible gas mixture therethrough. Thus, in the illustrativeembodiment, a metallic orifice plate 20 is fitted over a plurality ofmounting bolts 21 projecting longitudinally from the rear end of theburner 10, and secured thereto by nuts 22 threaded onto the bolts 21.The head ends of the bolts 21 may be embedded within the refractorymaterials contained within the metal housing 12 during the formation andassembly thereof. To provide a gas tight seal between the orifice plate20 and the burner housing 12, a gasket 23 is preferably placedtherebetween.

It is important to note that the open area of the orifice leading intothe inlet end of the combustion tunnel must be relatively small in orderto prevent the flame within the combustion tunnel from flashing backinto the equipment upstream of the tunnel. Thus, in order to increasethe width of the orifice, as is required to produce an attenuating blastsufficiently wide for the greater number of primary filaments that canbe produced from the modern melting pots, corresponding reductions mustbe made in the vertical dimension of the orifice. For example, in oneembodiment of the invention, an increase in the width of the orifice to8% inches required the height of the orifice to be reduced to 0.094inch. While such a restricted orifice is of significant value inpreventing flashbacks, it makes it extremely difficult to provide therequired gas velocity and flow rate through the orifice into thecombustion tunnel.

Accordingly, one of the important features of the present invention isthe provision of a plenum unit 30 for supplying the combustible gasmixture to the burner through the orifice so that high throughput ratesand velocities can be achieved even through extremely restrictedorifices. The plenum unit connects the orifice to a conduit throughwhich a combustible gas mixture is supplied and is designed to deliverthe combustible gas mixture uniformly across the orifice whilegenerating minimum turbulence and having minimum pressure loss. Theplenum unit is designed to cause the flow of the combustible gas mix tobe laminar in nature, that is, to be substantially free of all eddiesand turbulence. This construction provides a high volume flow of gaswith minimum loss of pressure in the transition. Additionally, thedischarge from the orifice is uniform. Furthermore, because a largerproportion of the pressure from the supply system can be applied to theorifice, the orifice can be made of smaller cross sectional area. Thiscauses the combustible gas mixture to issue from the orifice at a highervelocity for any given volume flow, leading to better combustioncharacteristics within the refractory tunnel, In addition, the highervelocity aids in preventing flashback of the flame into the supplysystem, the condition which occurs when the velocity of the advance ofthe combustive mixture falls below the velocity of propagation of theflame as determined by the particular mixture of gaseous fuel and airbeing used. The construction of the plenum unit from a thermallyconductive material also aids in preventing flashback. A flame frontpropagating upstream into the orifice and against a velocity flow ofcombustible mixture which is less than the velocity of flame propagatingcomes into contact with a cool surface, which, by its conductive nature,reduces such flame front below its ignition temperature, thus quenchingthe flame. These features of the invention thereby provide a burneroperable efficiently and safely over a wide range of operatingconditions.

In the preferred embodiments of the invention, the plenum unit 30includes an entranceway 31 (FIGS. 3 and 4) which is substantiallycoextensive with the discharge opening of a supply conduit 32 connectedto a source (not shown) of a combustible gas mixture such as fuel andair. The entranceway 31 may be connected to the supply conduit 32 in anysuitable manner, such as that illustrated in FIG. 4, but it is preferredto maintain the inner surface of the interconnection as smooth aspossible to avoid the creation of turbulence in the gases flowingtherethrough.

It will be appreciated that the discharge opening of the supply conduit32 is considerably larger than the vertical dimension of the orificeassociated with the tunnel inlet opening 11a, and considerably narrowerthan the width of the orifice. To effect the transition between thesetwo disparate opening configurations, the walls of the plenum unit 30taper gradually outwardly in the direction corresponding to the width ofthe inlet orifice and the tunnel 11, as indicated at 33 in FIGS. 3 and4. After the walls of the plenum unit 30 have diverged to the full widthof the inlet Orifice, they are tapered gradually inwardly toward eachother in the direction corresponding to height of the inlet orifice, asindicated at 34 in FIG. 4, so that the exit end of the plenum unit issubstantially coextensive with the inlet orifice. It will be appreciatedthat this gradual transition from the cross sectional configuration ofthe supply conduit 32 to the cross sectional configuration of the inletorifice tends to avoid the creation of turbulent conditions within theplenum unit and, in fact, the plenum unit is specifically designed toprovide laminar flow of the gas mixture therethrough under the operatingconditions in which it is to be used. In other words, the dimensions andphysical configuration of the plenum unit 30- are designed to providelaminar flow when a given gas mixture is passed therethrough at a givenfluid velocity. As a result, the gas mixture is distributed uniformlyover substantially the entire area of the orifice at the exit end of theplenum unit 30, and can be discharged through the orifice into thecombustion tunnel at relatively high velocities and flow rates, and witha relatively small back pressure in the region between the supplyconduit 32 and the orifice plate 20. Thus, a high gas velocity and flowrate and low back pressure can be achieved even with extremelyrestricted orifices such as the 8% inches by 0.094 inch orificementioned previously. For example, in one embodiment of the illustrativedesign having the aforementioned orifice size and a tunnel 8% incheswide, inch high at the inlet opening, and /2 inch high at the outletopening, the back pressure within the plenum unit was found to vary from14 to 52 ounces per square inch when the gas flow rate was varied from500 to 1000 cubic feet per hour, which is significantly lower than theback pressure in burners known heretofore. The back pressure in thisexample Was measured by inserting a pressure gage through a smallaperture 40 ,4 inch) associated with a lateral coupling member 41, theaperture 40 and coupling member 41 being located adjacent a region ofrelatively low velocity within the plenum unit so as to measureprimarily static pressure.

It is understood that the foregoing description of the preferredembodiment of the invention is given for illustration purposes only. Itis recognized that the construction of the plenum unit may vary so longas the operational characteristics are maintained. Accordingly, the twostep change from the circular supply conduit 32 to the orifice 35, asillustrated in FIGS. 3 and 4, could be accomplished in one step providedthe laminar flow, h1gh throughput rates and velocities, and pressurescould be maintained. Also, it is recognized that changes in shape andsize of the supply conduit 32 would result in corresponding changes inthe shape of the plenum unit so as to obtain the above describedoperational characteristics. Furthermore, although the plenum unitillustrated in FIGS. 3 and 4 is curved, it is recognized that the unitif desired could be made straight. However, it is noted that significantresults, as described herein, have been achieved by the construction ofthe preferred embodiment as illustrated in FIGS. 3 and 4.

In addition to the increased gas velocities and flow rates and reducedback pressure, the laminar flow plenum unit provided by this inventionmaintains a relatively low temperature on the input side of the orificeplate 20, thereby providing a further safeguard against flashback. Forexample, with a temperature of 2600 F. at the entrance portion of therefractory tunnel, the temperature 1n the plenum unit 30 an inch or soupstream of the orifice plate 20 is typically in the range of about 100to 140 F. Furthermore, because of the restriction of the plenum unit asit approaches the orifice plate, to conform with the orificeconfiguration, a major portion of the outside surface of the orificeplate 20 is exposed to the ambient atmosphere to provide a further meansfor dissipating heat to maintain a low temperature in the areaimmediately adjacent the tunnel inlet opening.

Still another advantage of the present invention is that the turn downrange for the burner is virtually unlimited. That is, it has been foundthat the gas velocity at the inlet end of the combustion tunnel may bemaintained above the flame propagation speed until the off rate isapproached, i.e. with a natural gas and air mixture down to a rate ofabout 5 cubic feet of gas per hour. Even at the extremely low rates of 5cubic feet per hour or less, the flame is extinguished as soon as itpropagates into the orifice, by virtue of the fact that the heat isquickly absorbed and dissipated by the metal orifice plate and plenumunit due to the excellent heat transfer characteristics of thesecomponents. Consequently, the burner has an extremely wide range ofoperation with practically no danger of a flashback to the gas mixingequipment upstream of the burner.

In one working example of the present invention, the entranceway 31 ofthe plenum unit 30 was dimensioned to be coupled to a conventionaltwo-inch pipe. The lateral expansion in the direction of the tunnelorifice, i.e., section 33 of the unit 30, began 2%. inches from the endof the entranceway and flared from a width of 2 inches to a width of 8%inches (as viewed in FIG. 3) with the constant dimension (see FIG. 4)being 1% inches. In section 34 of the plenum unit 30, the Width wasmaintained constant at 8% inches, while the dimension corresponding tothe orifice height was gradually reduced from 1% inches to 0.094 inch.The tunnel and orifice dimenions were the same as mentioned previously.

In accordance with one particular aspect of this invention, the exit endof the plenum unit extends through the orifice plate so that the exitopening of the plenum unit forms the orifice for admitting thecombustible gas mixture into the combustion tunnel. Thus, in theillustrative embodiment, the exit end 35 of the plenum unit 30 extendsthrough a complementally formed opening in the orifice plate 20 andterminates flush with the inside surface thereof. This construction hasthe advantage of providing a smooth uninterrupted surface all the wayfrom the supply conduit 32 to the inlet end of the combustion tunnel 11,thereby further insuring against any turbulence or interruption of thelaminar flow in this critical region.

It will be understood that the term plenum unit is used herein becausethe unit 30 serves as a means of distributing the combustile gas mixturefrom the main conduit to the input orifice.The plenum unit provided bythis invention diifers from most conventional plenum chambers, however,in that it is specifically designed to provide laminar flow, rather thanturbulent flow, in the transition region between the supply conduit andthe input orifice.

As can be seen from the foregoing detailed description, this inventionprovides an improved burner apparatus and method which is capable ofproviding the relatively high flow rates required for wide combustiontunnels, and without the danger of flashbacks. The gas velocity can bemaintained above the flame propagation speed over a Wide range of flowrates, including relatively low flow rates such as are encounteredduring burner turn down. Furthermore, a low back pressure is maintainedupstream of the tunnel inlet, and the temperatures in this same regionare also maintained at a low level so as to provide a further safeguardagainst flashback. In addition, the burner can be manufactured at a lowcost from readily available materials, and has a long operationalservice life. In fact, even when it becomes necessary to replace therefractory materials within the tunnel portion of the burner, it is notnecessary to replace the orifice plate and the plenum unit; these lattercomponents most conventionally are made of metal, and can be simplyconnected to a new tunnel structure. This operation can be repeated manytimes before it is necessary to replace the orifice plate and/ or theplenum unit.

It is to be understood that all the details in the foregoing descriptionof the invention need not be strictly adhered to and that variouschanges and modifications may suggest themselves to one skilled in theart, all falling within the scope of the invention as defined by thesuboined claims.

What I claim is: i 1. A burner apparatus for use in the flameattenuation of glass filaments, said apparatus comprising thecombination of a refractory combustion tunnel having laterally elongatedinlet and outlet openings, said inlet opening have a vertical dimensiongreater than that of the outlet opening and said tunnel having a Walltaperin-g inwardly from the inlet opening towards the outlet opening, anorifice plate at the inlet end of said tunnel and defining a laterallyelongated and vertically restricted orifice for admitting a combustiblegas mixture into said tunnel, a supply conduit for providing saidcombustible gas mixture, a plenum unit between said supply conduit andsaid orifice plate, with an exit end of said plenum unit beingsubstantially coextensive With said orifice, a portion of said plenumunit adjacent said exit end being of gradually increasing transversecross sectional configuration in the direction from said exit end towardsaid supply conduit and means associated with said plenum unit foracting on said combustible gas mixture after it leaves said conduit sothat said combustible gas mixture as it moves through said orifice isdistributed uniformly throughout its lateral and vertical extent and sothat it is substantially free of all eddies and turbulence.

2. A burner apparatus for use in the flame attenuation of glassfilaments, said apparatus comprising the combination of a refractorycombustion tunnel having laterally elongated inlet and outlet openings,an orifice plate at the inlet end of said tunnel and defining alaterally elongated and vertically restricted orifice for admitting acombustible gas mixture into said tunnel, a supply conduit for providingsaid combustible gas mixture, a plenum unit between said supply conduitand said orifice plate with an exit end of said plenum unit beingsubstantially coextensive with said orifice, a portion of said plenumunit adjacent said exit end being of gradually increasing transversecross sectional configuration in the direction from said exit end towardsaid supply conduit so that said combustible gas mixture as it movesthrough said orifice is distributed uniformly throughout its lateral andvertical extent and so that it is substantially free of all eddies andturbulence.

3. A burner apparatus as set forth in claim '2 wherein said orificeplate is made of metal.

4. A burner apparatus as set forth in claim 2 wherein said plenum unitis made of metal.

5. A burner apparatus as set forth in claim 2 wherein the width of saidorifice is considerably greater than the corresponding dimension of thedischarge opening of said supply conduit and the height of said orificeis considerably smaller than the corresponding dimension of thedischarge opening of said supplyconduit.

6. A burner apparatus as set forth in claim 2 wherein the exit end ofsaid plenum unit extends through said orifice plate so that the exitopening of the plenum unit forms the orifice for admitting said gasmixture into said tunnel.

7. A burner apparatus as set forth in claim 2 wherein said orifice isvertically positioned closer to the upper edge of said inlet opening ofsaid tunnel than to the lower edge of said inlet opening.

8. A burner apparatus as set forth in claim 2 wherein the verticaldimension of said inlet opening of said tunnel is greater than thevertical dimension of said outlet opening, and the bottom wall of saidtunnel is tapered upwardly from the lower edge of said inlet openingtoward said outlet opening.

9. A burner apparatus for use in the flame attenuation of glassfilaments, said apparatus comprising the combination of a refractorycombustion tunnel having laterally elongated inlet and outlet openings,a thermally coductive orifice plate at the inlet end of said tunnel anddefining a laterally elongated and vertically restricted orifice foradmitting a combustible gas mixture into said tunnel, a supply conduitfor said combustible gas mixture with a discharge opening having atransverse cross sectional configuration substantially greater than thetransverse cross sectional configuration of said orifice, and a plenumunit having an entranceway adjacent said discharge opening of saidconduit and connected thereto for receiving said combustible gas mixturefrom said conduit, said plenum unit havin an exit substantiallycoextensive with said orifice and connected thereto for passing said gasmixture through said orifice into said tunnel, and the walls of saidplenum unit between said entranceway and said exit being graduallytapered in the direction from said entranceway to said exit to act onsaid combustible gas mixture as it passes through said plenum unit sothat said combustible gas mixture as it passes through said orifice isdistributed uniformly throughout the lateral and vertical extentthereof, has substantially no eddies or turbulence therein, and hassuffered substantially no loss of pressure.

10. A burner apparatus as set forth in claim 9 in which said orifice hasa uniform vertical dimension of about 0.1 inch or less across the entirewidth thereof.

11. A burner apparatus as set forth in claim '10 in which said orificehas a width of at least 8 inches.

12. A burner apparatus as set forth in claim 9 wherein said orifice isvertically positioned closer to the upper edge of said inlet opening ofsaid tunnel than to the lower edge of said inlet opening.

13. A burner apparatus as set forth in claim 9 wherein the exit end ofsaid plenum unit extends through a complementally formed opening in saidorifice plate so that the exit opening of the plenum unit forms saidorifice for admitting the gas mixture into the combustion tunnel.

References Cited UNITED STATES PATENTS 2,623,579 12/1952 Furkert 43l-353 3,048,217 8/1962 Denniston 65-16 3,327,503 6/1967 Labino 6516 S.LEON BASHORE, Primary Examiner R. L. LINDSAY, 1a., Assistant ExaminerUS. Cl. X.R. 6516; 431-353

